Process for producing reinforced nonwoven fabrics

ABSTRACT

Textile-length fibers are subjected to a centrifugal force which orients them in a lateral direction, in which orientation they are deposited upon and mechanically engaged with a set of spacedapart warp strands to form novel nonwoven fabrics.

United States Patent 1 1 [111 3,862,867

Marshall 1 Jan. 28, I975 1 PROCESS FOR PRODUCING REINFORCED NONWOVEN FABRICS 156] References Cited [75] Inventor: Preston I". Marshall, Walpole, Muss. I UNITED STATES PATENTS 2,986,780 6/1961 lilctlinger 19/156 3 t [7 Asslgnee {Alt-Kendall Lompany W1lpole 2.996.]02 Q M schuucr llllllll 3.220.811 11/1965 Schuller [-22] Filed; June 27, I973 3.716 430 2/1973 Croon et ul..... 3.765971 10/1973 l-lcissner 156/622 [21] Appl. No.: 374,003 Related A pli ti D t Primary Examiner-Daniel J. Fritsch [62] DivisionofSer. No. 256,711. May 25. 1972, Put. No.

3.816.231. [57] ABSTRACT Y Textile-length fibers are subjected to a centrifugal [52] 156/621 19/1563 156/74 force which orients them in a lateral direction, in

, 156/181 264/121 which orientation they are deposited upon and me- [51] Int. CL... D0lg 25/00 Chunicully engaged with a set of spuced apurt Warp [58] Field of Search 156/622, 62.4, 62.6, 74, Strands form novel nonwoven fabrics 4 Claims, 6 Drawing Figures PATENTED A 5 sum 10F 3 FIG. 3

PATENTEB JAN 2 81975 SHEET 2 OF 3 PATENTED JAN28 i975 sum 30F 3 PROCESS FOR PRODUCING REINFORCED NONWOVEN FABRICS This application is a division of Ser. No. 256,711, filed y 25,, 19.72.11.032 U.S. Pat. N ,23

This invention relates to novel nonwoven fabrics, and to a process therefor. More particularly it relates to nonwoven fabrics comprising a spaced-apart set of warp strands running along the length of the fabric, with a web of textile-length fibers disposed substantially normal to said warp strands, a substantial number of said textile-length fibers being interlaced or otherwise mechanically engaged with said warp strands.

DISCUSSION OF PRIOR ART 1n the preparation of nonwoven fabrics wherein a,

substantial degree of tensile strength, toughness, and opacity are desired, as for use indisposable-garments, hospital drapes, and the like, it is common practice to laminate together nonwoven fabrics composed of textile-lengthfibers with other sheet material such as cellulose tissue, plastic films, paper, or other, continuous.

sheetmaterial. Such laminates, however, are usually deficient in tensile, strength 'unless semi-rigid binder materials are employed inthe lamination, in which case the laminate is liable to be unpleasantly stiff and pa pery, lacking in drape and esthetic appeal. In, such cases,- in order to, combine adequate tensile strength with soft polymeric binder material in, a product with suitable drape and conformability, recourse is frequently had to the use of an internalreinforcing layer or layers of textile yarns, spun or continuous filament.

Such a reinforcing layer maybe in the form of woven gauze or scrim, but due to the relative expense of woven fabrics, a more frequent reinforcement expedient is the use of a layer of warp strands crossed physically by, but not interwoven with, a layer or layers of.

filling strands which may be normally disposed to the warp strands, or. disposed at an angle or angles thereto. In order to impart stability to such an array, the multiple sets of yarns are commonly .bonded to each other at at least a portion of their crossover points.

Prior art yarn-reinforcing devicesof this nature, however, are intricate, expensive, difficult to maintain, and,

are rarely capableof operating at the speed at which it isdesired to produce nonwoven fabrics in order to make them economically. feasible for use in disposable garments.

BACKGROUNDOF THE INVENTION One obvious way to facilitate the processing of non- Further objects of the invention will be apparent from the following description and. drawings, in which:

FIG. 1 is a perspective view of a product of this invention.

FIG. 2 is a similar view of the product of FIG. 1 showing in detail the nature of the mechanical engagement of fibers and warp strands.

FIG. 3 is an enlarged view of another embodiment of the invention.

FIG. 4 is a side elevation of an apparatus suitable for carrying out the process of the invention.

FIG. 5 is a top elevation of the apparatus of FIG. 4.

FIG. 6 is a side elevation of the centrifugal or horn section of FIG. 4.

Basically, the process comprises the formation of a high-velocity fluid stream of textile-length fibers, diffusion and deceleration of the fibrous stream in achamber that is of substantial width in comparison with its thickness, to form a relatively wide but shallow fibrous stream, and then deflecting the fluid stream of fibers along a transversely extended smoothly curved surface curved in the direction of the stream, the curved surface forming what will herein be termed a horn.

In this manner, centrifugal force is exerted on the fibers, causing them to align in a transverse direction along the curved surface and to concentrate in a narherein by reference, said application being a continuawoven fabrics and laminates with strand reinforcement would be to omit the time-consuming need for crossstrand reinforcement, using only a set of spaced-apart warp strands. However, unless the warp strands are spaced very closely together, there is no support for that portion of an overlay, such as a tissue, lyingbetween the warp strands. Spacing the warp strands closely together is economically inexpedient: furthermore, no cross-directionv (C.D.) strength is provided.

It is an object of this invention to provide a primarily two-dimensional nonwoven fabric comprising a set of spaced-apart warp strands, reinforced in the cross di rection by a planar webof textile-length fibers, the tex tile length fibers being predominantly oriented normal to the warp strands, and a portion of said fibers being mechanically engaged with said warp strands.

tion-in-part of U.S. Ser. No. 196,709, filed Nov. 8, 1971.

The essenceof the present invention is the interposi tion of a set of spaced-apart warp strands which traverse'thelower edge of the centrifuge or horn, in a direction substantially normal to the flow of the narrow band of transversely-aligned fibers. The spacing of the strands and the length of the fibers are so chosen that at least a portion of the fibers, traveling at high velocity as they reach the forward'exit edge of the horn, become mechanically engaged with the warp strands and with each other. Thus a set of parallel warp strands, having no crosswise tensile strength per se, is converted into a nonwoven fabric, with a strand warp and a fibrous fillingsubstantially'normal thereto. The nature of the mechanical engagement will be more fully explained below.

TECHNICAL DISCLOSURE By warp'strands is meant herein a spaced-apart noninterconnected set of supportive and reinforcing strands, of substantial tensile strength, running in the machine (M.D.) or longitudinal direction ofthe fabric. Exemplary but not restrictive illustrations are spun yarns, continuous filament yarns, narrow ribbons of film, fine wires, and bands of spread-apart tow comprising continuous synthetic filaments.

By textile-length fibers is meant fibers between 1 /2 and about 6 inches in length, capable of being formed into a fluid stream of substantially individualized fibers under the influence of an airjet.

Referring to FIG. 4 there is shown a fluid-powered jet or aspirator, l0, capable of converting a top or sliver of staplelength fibers into a high-velocity fluid stream of substantially individualized fibers. Such jets, their parameters, and their function are described in detail in my copending applications Ser. Nos. 159,229, filed July 2, 1971, now US. Pat. No. 3,793,679 and 164,255, filed July 20, l97l, now US. Pat. No. 3,727,270, and there are also commercially available aspirators capable of performing a similar function.

The high-velocity fluid stream of fibers is directed into the entry chamber 12, and thence is diffused into a guiding chamber 14, which, as seen by comparing FIGS. 4 and 5, reforms the fibrous stream into a stream which is wider and shallower than the diffuse stream emerging from the aspirator. The wide and shallow fibrous stream flowsthen then through the chamber 16 and preferably to a constricting region 18, which acts as a Venturi. While not absolutely mandatory, this constriction 18 serves to iron out or minimize local disruptive pressure differences or vortices, thus evening out the flow of fibers.

From the Venturi section 18 the fibrous stream passes into the curved centrifuge section 22, where the actual reorientation takes place. The majority of the fibers are thrown against the leading or forward contour of the centrifuge 22, causing them to become reoriented from their previous orientation parallel to the fluid stream, or long axis of the apparatus, to a position in which they lie predominantly across or normal to the direction of fluid flow.

Immediately adjacent to and preferably in contact with the exit section of the horn, a warp of spaced-apart strands 25, from supply roll 23, is caused to traverse the exitsection in a direction normal to the fiber flow. As seen more clearly in FIG. 6, the reoriented fibers are flowing in a narrow band traversing downwardly along the forward section of the horn. This band is custom: arily so narrow as to be less in width than the length of an individual fiber.

In preferred operation, the operating air pressures and apparatus configuration are such that the air velocity in the Venturi section 18 is about 88 to 176 feet per second, and at the forward edge of the exit section of and 38. In order to bleed off excess air, and to allow high air volumes and velocities to be employed in the horn, a conventional suction box 27 may be mounted immediately below the screen, as shown in FIG. 4.

Also, in order to prevent leakage of air into the exit section of the horn, as shown in FIGS. 4 and 6, a sealing roll 28 may rotate across the leading edge of the exit section of the horn, contacting the warp strands, and a curved plastic strip may make similar contact with the warp strands along the rear edge of the exit section.

The warp strand-textile length fiber combination may conveniently be doffed by means of take-off rolls 32 and 34, whence it is woundup by conventional means, not shown.

The size of the apparatus will naturally vary with the width of fabric to be produced, the volume of fiber to .be processed, and with other factors. A typical set of dimensions might involve an entry chamber 12 in the form of a 10 inch-cube. The guiding chamber 14 may taper down to a 4.5 inch depth, while widening out to 40 inches for the purpose of producing a 40 inch-wide web. The chamber 16 may be 40 inches square and 4.5

the horn, where the fibers are grouped in a narrow Y transverse band, the air velocity is from about 44 to 88 feet per second. In this manner the fibers are strongly impelled onto the warp strands, and become mechanically engaged therewith as explained more fully below.

It should be appreciated that when the fibrous web is described as being oriented substantially normal to the warp strands, this does not mean that the fibers are laid down absolutely straight and parallel, like a row of matchsticks, since the length of the fibers being dealt with herein is so much greater than their diameter, and the fibers are so flexible, that practically without exception every fiber will lie in a twisted and cursive path, with curves and direction reversals along its path. The mean orientation of the fibers, therefore, is measured by the ratio of MD. to CD. strength of the fibrous web per se. By the statement herein that the fibers are predominantly oriented normal to the warp strands is meant that the ratio of CD. to MD. strength in the fibrous web alone is at least 4 or 5 to I.

As desirable auxiliary equipment, means may be supplied to prevent excessive downward deflection of the warp strands as they traverse the exit section of the horn. This preferably is in the form of an air permeable conveyor, such as a screen, 24, driven by drive rolls 36 inches deep, with a capacity of ISO-cubic inches.

The outlet slot of the Venturi section 18 may taper down to a depth of about 1.2 inches, ejecting a fibrous stream into the 2 inch deep opening of the centrifugal section 22. The guiding surfaces of this centrifugal section 22 are curved in a 15 inch radius through a 90 turn, terminating in an outlet section 6 inches wide, thus giving a 240 square inch screen deposition area.

The above dimensional parameters are illustrative only, and not restrictive. Engineering details for modifications of the apparatus may be made, bearing in mind that the centrifugal force developed is proportional to the square of the velocity of the air stream, and inversely proportional to the radius of curvature.

NATURE OF THE PRODUCT The products of this invention are in general planar nonwoven fabrics of substantial length and breadth in comparison with their thickness. As shown in FIG. 1, they comprise a set of warp streands, strands, and a superimposed web or fleece of textile-length fibers 42, lying principally on and normal to the warp strands.

As mentioned previously herein, a portion of the fibers are mcehanically engaged with the warp strands. This is shown more clearly in FIG/2, wherein it may be assumed that that portion of the fibers of FIG. 1 which are not engaged with the warpstrands, but are merely lying across the strands, has been removed for clarity. The nature of the mechanical engagement with the warp strands is of three principal types. First, there is V a plain interlacing, as shown at 44, where a textilelength fiber passes above certain warp strands and below certain other warp strands. Second, there is a wrapping action of one end of a fiber around a strand, as shown at 46. Third, as shown at 48, certain portions of the length of a fiber may be formed into a loop or series of loops, which loops are then at least in part wrapped around one or more wrap strands.

Additionally, there is a certain degree of entanglement and wrapping of some fibers, which are not in mechanical engagement with the warp strands as described above, with and around certain other fibers which are so engaged. It will be appreciated that the greatest degree of mechanical engagement of fibers with warp strands occurs with the fibers initially deposited on the strands, and that as more and more textile fibers are-deposited,'they tend to lie upon the initially deposited portion of the fleece. Light weight nonwoven fabrics of this invention, therefore, will generally show greater tensile-strength per unit of fabric weight tha fabrics with a heavier deposit of fibers.

In general, in the practice of this invention, a set of I warp strands of, for example, spuncotton yarns, will be spaced from 0.5 to 1.5 inches apart, and will have applied thereto a fleece or web of textile-length fibers of from 1.5 to 6.0 inches in length, weighting from 5 or 6 to 60 or 70 grams per square yard. The invention will be illustrated by the following examples.

EXAMPLE 1 The apparatus employed was that shown in FIG. 4, wherein the ,warp strands were 40s 2 ply cotton yarns spaced approximately 0.75 inches apart.

The chamber 12 of FIGS. 4 and 5 was fed by 4 aspirator jets of the-type described as Type C in copending application Ser. No. 164,255, referred to above. The throat diameter of each jet was 0.562 inches indiameter, the taper was 2.7, and the exit section diameter was 0.600 inches. Each jet was powered by air at 75 P.S.I.G., which, as set forth in Ser. No. 164,255, develops a maximum vacuum in the tube, of approximately 24 inches of mercury.

Each jet was fed by a 60 grain rayon sliver, 1.5 denier per filament, 1 9/16 inches long. The total denier of the four ends of sliver was 153,060, and the feed rate was 4 feet per minute.

The 40 inch wide beam of cotton warp strands traversed the exit section of the horn at a speed of 8 feet per minute, in the manner shown in FIG 4.

The product resembled that shown in FIG. 1, with a portion of the cross-deposited fibers mechanically engaged with the warp strands, as shown in FIG. 2. The yarnfiber product weighed 8.7 grams per square yard, of which 2.9 grams was cotton yarn and 5.8 grams was rayon fiber. When a 1-inch wide strip was cut across the 40 inch width of thefabric and suspended by one end, the strip remained integral and self-sustaining in the absence of binder, indicating internal cohesion due to fiber-yarn interengagement.

If it is desired to produce stronger products, or to provide a potential adhesive property to fabrics of this invention, auxiliary binding material may be deposited within the product by the same air-deposition process. Such binding material may be in the form of thermoplastic fibers, or thermoplastic powders, or both, and the fiber-warp strand composite may be further unified by developing the adhesive properties of the auxiliary binding material, or the composite may be laminated to another planar sheet material, as shown in the following example.

EXAMPLE 2 The same apparatus, jets, rayon sliver, and cotton' axis of the pipe. Aspirators of this type are designed to operate at from 5 to 150 P.S.I.G., depending on the degree of vacuum it is desired to establish.

One CP 200 aspirator was fed with a supply of 3 denier 0.25 inch long Vinyon fibers (Union Carbide trademark fora copolymer of vinyl chloride-vinyl ace' tate in fiber form), at P.S.I.G., delivering 6 grams of short thermoplastic fiber to each square yard of product. The other C? 200 aspirator, operating at 20 P.S.I.G., delivered to each square yard of product ap proximately S'grams of a thermoplastic powder, 35 mesh, a copolymer of polyethylene-polyethylacrylate.

The composite product, after leaving the take-off roll 32 of FIG. 4, was plied with a layer of cellulose tissue weighing 20 grams per square yard, and was passed through a 3-roll calender. The bottom steel roll was heated to about 420F: the center silicone covered roll equilibrated at about 360F., and the top steel roll at about F. The tissue side made contact with the heated steel roll, and the pressure was about 70 pounds per inch of nip.

The final compodite product weighed 59 grams per square yard, of which 25 grams was rayon fiber, 20 grams tissue, 3 grams cotton yarn, 6 grams fused thermoplastic fiber, and 5 grams fused thermoplastic powder. It has a tensile strength of 6.4 pounds per inch wide strip cut to include one cotton warp strand, and a filling strength of 1.45 pounds.

Under the conditions of hot calendering, the thermoplastic fibers and thermoplastic powder granules were found, under microscopic examination, to have fused to binder globules unifying the rayon fibers, principally at their points of intersection, as shown at 50 in FIG. 30. Both thermoplastic components also served to bond the sheet of tissue to the assembly.

It will be apparent to those skilled in the art that any desired sheet material, such as film, foil, paper, or other nonwoven fabric, may be thus laminated to the basic fiber-warp strand-binder composite.

Having thus described my invention, I claim:

1. The process of making a nonwoven fabric which comprises passing a fluid-borne stream of textile-length fibers through a passageway having a transverselyextended smoothly curved surface curved in the direction of said stream,

thereby changing the direction of said fluid-borne stream along said surface and causing centrifugal force on said fibers to align :said fibers in a transverse direction along said surface and concentrating said fibers thereat in a narrow, transverselyextended band,

collecting said fibers of said band on a set of parallel,

spaced-apart warp strands, said warp strands extending continuously in the 1ongitudinal direction of said fabric,

and causing a portion of said fibers to entangle with said warp strands in mechanical engagement by passing over certain of said warp strands and under other of said warp strands,

and causing an additional portion of said fibers to entangle with said warp strands by having a portion of their length wrapped around at least a portion of the perimeters of certain of said strands.

2. The process according to claim 1 wherein a thermoplastic binder material is diffused into said fluidborne stream of fibers.

3. The process'according to claim 2 wherein the thermoplastic binder material is a powder.

4. The process according to claim 2 wherein the thermoplastic binder material is thermoplasticfibers. 

1. THE PROCESS OF MAKING A NONWOVEN FABRIC WHICH COMPRISES PASSING A FLUID-BORNE STREAM OF TEXTILE-LENGTH FIBERS THROUGH A PASSAGEWAY HAVING A TRANSVERSELY-EXTENDED SMOOTHLY CURVED SURFACE IN THE DIRECTION OF SAID STREAM, THEREBY CHANGING THE DIRECTION OF SAID FLUID-BORNE STREAM ALONG SAID SURFACE AND CAUSING CENTRIFUGAL FORCE ON SAID FIBERS TO ALIGN SAID FIBERS IN A TRANSVERSE DIRECTION ALONG SAID SURFACE AND CONCENTRATING SAID FIBERS THEREAT IN A NARROW, TRANSVERSELY-EXTENDED BAND, COLLECTING SAID FIBERS OF SAID BAND ON A SET OF PARALLEL, SPACED-APART WARP STRANDS, SAID WRAP STRANDS EXTENDING CONTINOUSLY IN THE LONGITUDINAL DIRECTION OF SAID FABRIC, AND CAUSING A PORTION OF SAID FIBERS TO ENTANGLE WITH SAID WARP STRANDS IN MECHANICAL ENGAGEMENT BY PASSING OVER CERTAIN OF SAID WARP STRANDS AND UNDER OTHER OF SAID WARP STRANDS, AND CAUSING AN ADDITIONAL PORTION OF SAID FIBERS TO ENTANGLE WITH SAID WARP STRANDS BY HAVING A PORTION OF THEIR LENGTH WRAPPED AROUND AT LEAST A PORTION OF THE PERIMETERS OF CERTAIN OF SAID STRANDS.
 2. The process according to claim 1 wherein a thermoplastic binder material is diffused into said fluid-borne stream of fibers.
 3. The process according to claim 2 wherein the thermoplastic binder material is a powder.
 4. The process according to claim 2 wherein the thermoplastic binder material is thermoplastic fibers. 